Cellulose Solutions in Ionic Liquids

ABSTRACT

The present invention relates to a solution comprising cellulose and an ionic liquid comprising anions and cations as solvent, wherein the cations comprise at least one atom selected from the group consisting of nitrogen, oxygen, sulfur and phosphorus which is present in protonated form, its preparation and use for physical and chemical treatment.

The present invention relates to a solution comprising cellulose and an ionic liquid as solvent, a process for preparing it and its use.

Cellulose is a very versatile raw material. In the textile industry, cellulose is, for example, the most important constituent of fiber raw materials, in particular of cotton.

Cellulose can be used unchanged or after physical or chemical treatment. In the latter two cases, it is advantageous for cellulose to be in preferably completely dissolved form in a solvent. However, cellulose is insoluble in most solvents.

Cellulose is soluble as a copper chelate complex in some copper solutions. Regenerated cellulose can be obtained by precipitation of the cellulose. However, such copper solutions are not very suitable as solvents for cellulose in the case of physical or chemical treatment of the cellulose.

For this reason, the systems known, inter alia, as ionic liquids in the literature were proposed very early on as solvents for cellulose.

Thus, U.S. Pat. No. 1,943,176 describes the dissolution of cellulose in benzylpyridinium chloride.

As an example of an ionic liquid, benzylpyridinium chloride is a salt which is present in molten form and thus as a liquid at comparatively low temperatures.

Ionic liquids are becoming increasingly important as solvents, e.g. for carrying out chemical reactions. Peter Wasserscheidt, Angew. Chem. 2000, 112, 3926-3945, for example, gives an overview of the use of ionic liquids in transition metal catalysis.

Ionic liquids which are present in the liquid state even at room temperature are described, for example, by K. N. Marsh et al., Fluid Phase Equilibria 219 (2004), 93-98, and J. G. Huddleston et al., Green Chemistry 2001, 3, 156-164.

DE-A 102 02 838 describes the use of ionic liquids for separating acids from chemical mixtures.

Owing to the good solvent capabilities of ionic liquids, their use for the dissolution of cellulose is also proposed in the more recent international patent application WO-A 03/029329. However, it is emphasized there that the ionic liquids should comprise cations which comprise a quaternary ammonium ion which should be quaternized by alkyl groups, in particular methyl.

Although the characteristics of the cellulose-comprising solution and its preparation described in WO-A 03/029329 have good results, there is a need to provide improved solutions.

It is therefore an object of the present invention to provide a solution of dissolved cellulose which displays improved properties.

The object is achieved by a solution comprising cellulose and an ionic liquid comprising anions and cations as solvent, wherein the cations comprise at least one atom selected from the group consisting of nitrogen, oxygen, sulfur and phosphorus which is present in protonated form.

It has been found that the preparation of cations by means of hydrogen (protonation), in particular by quaternization of the nitrogen, can result in improved properties. In particular, it has been found that solutions comprising ionic liquids are easier to work up. Thus, the ionic liquids can be converted by addition of a base into a distillable form, which makes them easier to separate off.

The protonation can be effected at one or more identical or different heteroatoms (N, O, S, P). Apart from generation of a positive charge by protonation, further positive charges can also be present in the cations, for example as a result of alkylation of a nitrogen.

However, the cations preferably have at least one nitrogen atom which is present in protonated form as ammonium cation.

The cellulose to be dissolved can originate from, for example, regenerated cellulose, fibrous cellulose, wood fibers, lint, cotton or paper.

It is preferred that, in the solution of the present invention, more than 1% by weight of cellulose, based on the total weight of the solution, are completely dissolved. More preferably, more than 3% by weight, particularly preferably more than 5% by weight and in particular at least 7% by weight, based on the total weight of the solution, are completely dissolved.

Advantageously, up to 35% by weight of cellulose, based on the total weight of the solution, can be completely dissolved. Furthermore, up to 25% by weight of cellulose, based on the total weight of the solution, can be completely dissolved. Solutions in which up to 15% by weight of cellulose are completely dissolved are especially suitable for particular applications.

For the purposes of the present invention, ionic liquids are preferably salts of the general formula

(A) salts of the general formula (I)

[A]_(n) ⁺ [Y]^(n−)  (I),

where n is 1, 2, 3 or 4, [A]⁺ is a quaternary ammonium cation, an oxonium cation, a sulfonium cation or a phosphonium cation and [Y]^(n−) is a monovalent, divalent, trivalent or tetravalent anion;

(B) mixed salts of the general formulae (II)

[A ¹]⁺ [A ²]⁺ [Y] ^(n−)  (IIa), where n=2;

[A ¹]⁺ [A ²]⁺ [A ³]⁺ [Y] ^(n−)  (IIb), where n=3;

[A ¹]⁺ [A ²]⁺ [A ³]⁺ [A ⁴]⁺ [Y] ^(n−)  (IIc), where n=4, and

where [A¹]⁺, [A²]⁺, [A³]⁺ and [A⁴]⁺ are selected independently from among the groups mentioned for [A]⁺, and [Y]^(n−) is as defined under (A); or

(C) mixed salts of the general formulae (III)

[A ¹]⁺ [A ²]⁺ [A ³]⁺ [M ¹]⁺ [Y] ^(n−)  (IIIa), where n=4;

[A ¹]⁺ [A ²]⁺ [M ¹]⁺ [M ²]⁺ [Y] ^(n−)  (IIIb), where n=4;

[A ¹]⁺ [M ¹]⁺ [M ²]⁺ [M ³]⁺ [Y] ^(n−)  (IIIc), where n=4;

[A ¹]⁺ [A ²]⁺ [M ¹]⁺ [Y] ^(n−)  (IIId), where n=3;

[A ¹]⁺ [M ¹]⁺ [M ²]⁺ [Y] ^(n−)  (IIIe), where n=3;

[A ¹]⁺ [M ¹]⁺ [Y] ^(n−)  (IIIf), where n=2;

[A ¹]⁺ [A ²]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIg), where n=4;

[A ¹]⁺ [M ¹]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIh), where n=4;

[A ¹]⁺ [M ⁵]³⁺ [Y] ^(n−)  (IIIi), where n=4; or

[A ¹]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIj), where n=3, and

where [A¹]⁺, [A²]⁺ and [A³]⁺ are selected independently from among the groups mentioned for [A]⁺, [Y]^(n−) is as defined under (A) and [M¹]⁺, [M²]⁺, [M³]⁺ are monovalent metal cations, [M⁴]²⁺ is a divalent metal cation and [M⁵]³⁺ is a trivalent metal cation.

The ionic liquids preferably have a melting point of less than 180° C. The melting point is more preferably in the range from −50° C. to 150° C., still more preferably in the range from −20° C. to 120° C. and most preferably below 100° C.

Compounds which are suitable for forming the cations [A]⁺ of ionic liquids are, for example, known from DE 102 02 838 A1. Thus, such compounds can comprise oxygen, phosphorus, sulfur or in particular nitrogen atoms, for example at least one nitrogen atom, preferably 1-10 nitrogen atoms, particularly preferably 1-5 nitrogen atoms, very particularly preferably 1-3 nitrogen atoms and in particular 1-2 nitrogen atoms. If appropriate, further heteroatoms such as oxygen, sulfur or phosphorus atoms can also be comprised. The nitrogen atom is a suitable carrier of the positive charge in the cation of the ionic liquid, from which a proton or an alkyl radical can then be transferred in equilibrium to the anion so as to produce an electrically neutral molecule.

If the nitrogen atom is the carrier of the positive charge in the cation of the ionic liquid, a cation can firstly be produced by quaternization of the nitrogen atom of, for example, an amine or nitrogen heterocycle in the synthesis of the ionic liquids. The quaternization can be effected by protonation of the nitrogen atom. Depending on the protonation reagent used, salts having different anions are obtained. In cases in which it is not possible to form the desired anion directly in the quaternization, this can be effected in a further step of the synthesis. For example, starting from an ammonium halide, the halide can be reacted with a Lewis acid to form a complex anion from the halide and Lewis acid. As an alternative, it is possible to replace a halide ion by the desired anion. This can be achieved by addition of a metal salt with precipitation of the metal halide formed, by means of an ion exchanger or by displacement of the halide ion by a strong acid (with liberation of the hydrogen halide). Suitable methods are described, for example, in Angew. Chem. 2000, 112, pp. 3926-3945, and the references cited therein.

Preference is given to compounds which comprise at least one five- or six-membered heterocycle, in particular a five-membered heterocycle, which has at least one nitrogen atom and, if appropriate, an oxygen or sulfur atom; particular preference is given to compounds which comprise at least one five- or six-membered heterocycle which has one, two or three nitrogen atoms and a sulfur or oxygen atom, very particularly preferably those having two nitrogen atoms. Preference is also given to aromatic heterocycles.

Particularly preferred compounds are ones which have a molecular weight of less than 1000 g/mol, very particularly preferably less than 500 g/mol and in particular less than 250 g/mol.

Furthermore, preference is given to cations which are selected from among the compounds of the formulae (IVa) to (IVw),

and oligomers comprising these structures.

Further suitable cations are compounds of the general formulae (IVx) and (IVy)

and oligomers comprising this structure.

In the abovementioned formulae (IVa) to (IVy),

the radical R is hydrogen; and

the radicals R¹ to R⁹ are each, independently of one another, hydrogen, a sulfo group or a carbon-comprising organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical which has from 1 to 20 carbon atoms and is unsubstituted or interrupted by from 1 to 5 heteroatoms or functional groups or substituted, with the radicals R¹ to R⁹ which are bound to a carbon atom (and not to a heteroatom) in the abovementioned formulae (IV) also being able to be halogen or a functional group; or

two adjacent radicals from the group consisting of R¹ to R⁹ can together also be a divalent, carbon-comprising organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical which has from 1 to 30 carbon atoms and is unsubstituted or interrupted by from 1 to 5 heteroatoms or functional groups or substituted.

In the definition of the radicals R¹ to R⁹, heteroatoms are in principle all heteroatoms which are formally able to replace a —CH₂—, —CH═, —C≡ or ═C═ group. If the carbon-comprising radical comprises heteroatoms, then preference is given to oxygen, nitrogen, sulfur, phosphorus and silicon. Preferred groups are, in particular, —O—, —S—, —SO—, —SO₂—, —NR′—, —N═, —PR′—, —PR′₂ and —SiR′₂—, where the radicals R′ are the remaining part of the carbon-comprising radical. The radicals R¹ to R⁹ can in the cases in which they are bound to a carbon atom (and not to a heteroatom) in the abovementioned formula (IV) also be bound directly via the heteroatom.

Possible functional groups are in principle all functional groups which can be bound to a carbon atom or a heteroatom. Examples of suitable functional groups are —OH (hydroxy), ═O (in particular as a carbonyl group), —NH₂ (amino), ═NH (imino), —COOH (carboxy), —CONH₂ (carboxamide), —SO₃H (sulfo) and —CN (cyano). Functional groups and heteroatoms can also be directly adjacent so that combinations of a plurality of adjacent atoms, for instance —O— (ether), —S— (thioether), —COO— (ester), —CONH— (secondary amide) or —CONR′— (tertiary amide) are also comprised, for example di-(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl or C₁-C₄-alkyloxy.

Halogens may be fluorine, chlorine, bromine and iodine.

The radicals R¹ to R⁹ are preferably, independently of one another,

-   -   hydrogen;     -   halogen;     -   a functional group;     -   C₁-C₁₈-alkyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles and/or interrupted by one or more oxygen         and/or sulfur atoms and/or one or more substituted or         unsubstituted imino groups;     -   C₂-C₁₈-alkenyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles and/or interrupted by one or more oxygen         and/or sulfur atoms and/or one or more substituted or         unsubstituted imino groups;     -   C₆-C₁₂-aryl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles;     -   C₅-C₁₂-cycloalkyl which is optionally substituted by functional         groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms         and/or heterocycles;     -   C₅-C₁₂-cycloalkenyl which is optionally substituted by         functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen,         heteroatoms and/or heterocycles; or     -   a five- or six-membered, oxygen-, nitrogen- and/or         sulfur-comprising heterocycle which is optionally substituted by         functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen,         heteroatoms and/or heterocycles; or

two adjacent radicals together form

-   -   an unsaturated, saturated or aromatic ring which is optionally         substituted by functional groups, aryl, alkyl, aryloxy,         alkyloxy, halogen, heteroatoms and/or heterocycles and         optionally interrupted by one or more oxygen and/or sulfur atoms         and/or one or more substituted or unsubstituted imino groups.

C₁-C₁₈-alkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably methyl, ethyl, 1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl, 3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl, 3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl, 3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl, 2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl, 3,3-dimethyl-2-butyl, heptyl, octyl, 2-etylhexyl, 2,4,4-tri-methylpentyl, 1,1,3,3-tetramethylbutyl, 1-nonyl, 1-decyl, 1-undecyl, 1-dodecyl, 1-tridecyl, 1-tetradecyl, 1-pentadecyl, 1-hexadecyl, 1-heptadecyl, 1-octadecyl, cyclopentylmethyl, 2-cyclopentylethyl, 3-cyclopentylpropyl, cyclohexylmethyl, 2-cyclohexylethyl, 3-cyclohexylpropyl, benzyl (phenylmethyl), diphenylmethyl (benzhydryl), triphenylmethyl, 1-phenylethyl, 2-phenylethyl, 3-phenylpropyl, α,α-dimethylbenzyl, p-tolylmethyl, 1-(p-butylphenyl)ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylethyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1,2-di(methoxycarbonyl)ethyl, methoxy, ethoxy, formyl, 1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl, 3-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl, 6-methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethylaminobutyl, 6-dimethylaminohexyl, 2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl, 6-ethoxyhexyl, acetyl, C_(n)F_(2(n−a)+(1−b))H_(2a+b) where n is from 1 to 30, 0≦a≦n and b=0 or 1 (for example CF₃, C₂F₅, CH₂CH₂—C_((n−2))F_(2(n−2)+1), C₆F₁₃, C₈F₁₇, C₁₀F₂₁, C₁₂F₂₅), chloromethyl, 2-chloroethyl trichloromethyl, 1,1-dimethyl-2-chloroethyl, methoxymethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, 2-methoxyisopropyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenylthioethyl, 5-hydroxy-3-oxapentyl, 8-hydroxy-3,6-dioxaoctyl, 11-hydroxy-3,6,9-trioxaundecyl, 7-hydroxy-4-oxaheptyl, 11-hydroxy-4,8-dioxaundecyl, 15-hydroxy-4,8,12-trioxapentadecyl, 9-hydroxy-5-oxanonyl, 14-hydroxy-5,10-dioxatetradecyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-dioxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

C₂-C₁₈-Alkenyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles and/or interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups is preferably vinyl, 2-propenyl, 3-butenyl, cis-2-butenyl, trans-2-butenyl or C_(n)F_(2(n−a)−(1−b))H_(2a−b) where n≦30, 0≦a≦n and b=0 or 1.

C₆-C₁₂-Aryl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, isopropylphenyl, tert-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropyinaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorphenyl, 4-bromophenyl, 2-nitrophenyl, 4-nitrophenyl, 2,4-dinitrophenyl, 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl, ethoxyethylphenyl, ethoxymethylphenyl, methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl or C₆F_((5−a))H_(a) where 0≦a≦5.

C₅-C₁₂-Cycloalkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl, C_(n)F_(2(n−a)−(1−b))H_(2a−b) where n≦30, 0≦a≦n and b=0 or 1 or a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl.

C₅-C₁₂-Cycloalkenyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably 3-cyclopentenyl, 2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl or C_(n)F_(2(n−a)−3(1−b))H_(2a−3b) where n≦30, 0≦a≦n and b=0or 1.

A five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is preferably furyl, thiophenyl, pyrryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl, dimethylpyrryl, methoxyfuryl, dimethoxypyridyl or difluoropyridyl.

If two adjacent radicals together form an unsaturated, saturated or aromatic ring which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles and optionally interrupted by one or more oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups, the two radicals together are preferably 1,3-propylene, 1,4-butylene, 1,5-pentylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propenylene, 3-oxa-1,5-pentylene, 1-aza-1,3-propenylene, 1-C₁-C₄-alkyl-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene, 1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene.

If the abovementioned radicals comprise oxygen and/or sulfur atoms and/or substituted or unsubstituted imino groups, the number of oxygen and/or sulfur atoms and/or imino groups is not subject to any restrictions. In general, there will be no more than 5 in the radical, preferably no more than 4 and very particularly preferably no more than 3.

If the abovementioned radicals comprise heteroatoms, there is generally at least one carbon atom, preferably at least two carbon atoms, between any two heteroatoms.

The radicals R¹ to R⁹ are particularly preferably, independently of one another,

-   -   hydrogen;     -   unbranched or branched C₁-C₁₈-alkyl which is unsubstituted or         substituted by one or more hydroxy, halogen, phenyl, cyano,         C₁-C₆-alkoxycarbonyl and/or sulfonic acid substituents and has a         total of from 1 to 20 carbon atoms, for example methyl, ethyl,         1-propyl, 2-propyl, 1-butyl, 2-butyl, 2-methyl-1-propyl         (isobutyl), 2-methyl-2-propyl (tert-butyl), 1-pentyl, 2-pentyl,         3-pentyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-2-butyl,         3-methyl-2-butyl, 2,2-dimethyl-1-propyl, 1-hexyl, 2-hexyl,         3-hexyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl,         4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl,         4-methyl-2-pentyl, 2-methyl-3-pentyl, 3-methyl-3-pentyl,         2,2-dimethyl-1-butyl, 2,3-dimethyl-1-butyl,         3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, 2,3-dimethyl-2-butyl,         3,3-dimethyl-2-butyl, 1-heptyl, 1-octyl, 1-nonyl, 1-decyl,         1-undecyl, 1-dodecyl, 1-tetradecyl, 1-hexa-decyl, 1-octadecyl,         2-hydroxyethyl, benzyl, 3-phenylpropyl, 2-cyanoethyl,         2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl,         2-(n-butoxycarbonyl)ethyl, trifluoromethyl, difluoromethyl,         fluoromethyl, pentafluoroethyl, heptafluoropropyl,         heptafluoroisopropyl, nonafluorobutyl, nonafluoroisobutyl,         undecylfluoropentyl, undecylfluoroisopentyl, 6-hydroxyhexyl and         propylsulfonic acid;     -   glycols, butylene glycols and oligomers thereof having from 1 to         100 units and a hydrogen atom or a C₁-C₈-alkyl group as end         group, for example R̂O—(CHR^(B)—CH₂—O)_(n)—CHR^(B)—CH₂— or         R̂O—(CH₂CH₂CH₂CH₂O)_(n)—CH₂CH₂CH₂CH₂O— where R^(A) and R^(B) are         preferably hydrogen, methyl or ethyl and n is preferably from 0         to 3, in particular 3-oxabutyl, 3-oxapentyl, 3,6-dioxaheptyl,         3,6-dioxaoctyl, 3,6,9-trioxadecyl, 3,6,9-trioxaundecyl,         3,6,9,12-tetraoxatridecyl and 3,6,9,12-tetraoxatetradecyl;     -   vinyl; and     -   N,N-di-C₁-C₆-alkylamino, for example N,N-dimethylamino and         N,N-diethylamino.

The radicals R¹ to R⁹ are very particularly preferably, independently of one another, hydrogen or C₁-C₁₈-alkyl, for example methyl, ethyl, 1-butyl, 1-pentyl, 1-hexyl, 1-heptyl, 1-octyl, phenyl, 2-hydroxyethyl, 2-cyanoethyl, 2-(methoxycarbonyl)ethyl, 2-(ethoxycarbonyl)ethyl, 2-(n-butoxycarbonyl)ethyl, N,N-dimethylamino, N,N-diethylamino, chlorine or CH₃O—(CH₂CH₂O)_(n)—CH₂CH₂— and CH₃CH₂O—(CH₂CH₂O)_(n)—CH₂CH₂— where n is from 0 to 3.

Very particularly preferred pyridinium ions (IVa) are those in which

-   -   one of the radicals R¹ to R⁵ is methyl, ethyl or chlorine and         the remaining radicals R¹ to R⁵ are hydrogen;     -   R³is dimethylamino and the remaining radicals R¹, R², R⁴ and R⁵         are hydrogen;     -   all radicals R¹ to R⁵ are hydrogen;     -   R² is carboxy or carboxamide and the remaining radicals R¹, R²,         R⁴ and R⁵ are hydrogen; or     -   R¹ and R² or R² and R³ are together 1,4-buta-1,3-dienylene and         the remaining radicals R¹, R², R⁴ and R⁵ are hydrogen;

and, in particular, those in which

-   -   R¹ to R⁵ are hydrogen; or     -   one of the radicals R¹ to R⁵ is methyl or ethyl and the         remaining radicals R¹ to R⁵ are hydrogen.

Very particularly preferred pyridinium ions (IVa) are pyridinium, 2-methylpyridinium, 2-ethylpyridinium, 5-ethyl-2-methylpyridinium and 2-methyl-3-ethylpyridinium.

Very particularly preferred pyridazinium ions (IVb) are those in which

-   -   R¹ to R⁴ are hydrogen; or     -   one of the radicals R¹ to R⁴ is methyl or ethyl and the         remaining radicals R¹ to R⁴ are hydrogen.

Very particularly preferred pyrimidinium ions (IVc) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl; or     -   R¹ is hydrogen, methyl or ethyl, R² and R⁴ are methyl and R³ is         hydrogen.

Very particularly preferred pyrazinium ions (IVd) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl;     -   R¹ is hydrogen, methyl or ethyl, R² and R⁴ are methyl and R³ is         hydrogen;     -   R¹ to R⁴ are methyl; or     -   R¹ to R⁴ are methyl or hydrogen.

Very particularly preferred imidazolium ions (IVe) are those in which

-   -   R¹ is hydrogen, methyl, ethyl, 1-propyl, 1-butyl, 1-pentyl,         1-hexyl, 1-octyl, 2-hydroxyethyl or 2-cyanoethyl and R² to R⁴         are each, independently of one another, hydrogen, methyl or         ethyl.

Very particularly preferred imidazolium ions (IVe) are 1-methylimidazolium, 1-ethylimidazolium, 1-n-butylimidazolium, 1-n-octylimidazolium, 1-n-dodecyl-imidazolium, 1-n-tetradecylimidazolium, 1-n-hexadecylimidazolium, 1,2-dimethyl-imidazolium, 1,4-dimethylimidazolium, 2-methylimidazolium, 3-methylimidazolium, 3-etylimidazolium, 3-n-butylimidazolium, 3-octylimidazolium, 4-methylimidazolium, 2-ethylimidazolium, 1-vinylimidazolium, 1-n-octyl-4-methylimidazolium and 1,4,5-trimethylimidazolium.

Very particularly preferred pyrazolium ions (IVf), (IVg) or (IVg′) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² to R⁴ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred pyrazolium ions (IVh) are those in which

-   -   R¹ to R⁴ are each, independently of one another, hydrogen or         methyl.

As very particularly preferred pyrazolium ions, mention may be made of pyrazolium and 1,4-dimethylpyrazolium.

In the process of the invention, very particularly preferred 1-pyrazolinium ions (IVi) are those in which

-   -   R¹ to R⁶ are each, independently of one another, hydrogen or         methyl.

Very particularly preferred 2-pyrazolinium ions (IVj) or (IVj′) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁶ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred 3-pyrazolinium ions (IVk) or (IVk′) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R³ to R⁶ are each, independently of         one another, hydrogen or methyl.

Very particularly preferred imidazolinium ions (IVl) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl, 1-butyl or phenyl, R³ and R⁴ are each,         independently of one another, hydrogen, methyl or ethyl and R⁵         and R⁶ are each, independently of one another, hydrogen or         methyl.

Very particularly preferred imidazolinium ions (IVm) or (IVm′) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl or ethyl and R³ to R⁶ are each, independently of one         another, hydrogen or methyl.

Very particularly preferred imidazolinium ions (IVn) or (IVn′) are those in which

-   -   R¹ to R³ are each, independently of one another, hydrogen,         methyl or ethyl and R⁴ to R⁶ are each, independently of one         another, hydrogen or methyl.

Very particularly preferred thiazolium ions (IVo) or (IVo′) and oxazolium ions (IVp) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² and R³ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred 1,2,4-triazolium ions (IVq), (IVq′) or (IVq″) are those in which

-   -   R¹ and R² are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R³ is hydrogen, methyl or phenyl.

Very particularly preferred 1,2,3-triazolium ions (IVr), (IVr′) or (IVr″) are those in which

-   -   R¹ is hydrogen, methyl or ethyl and R² and R³ are each,         independently of one another, hydrogen or methyl, or R² and R³         are together 1,4-buta-1,3-dienylene.

Very particularly preferred pyrrolidinium ions (IVs) are those in which

-   -   R¹ is hydrogen, methyl, ethyl or phenyl and R² to R⁹ are each,         independently of one another, hydrogen or methyl.

Very particularly preferred imidazolidinium ions (IVt) are those in which

-   -   R¹ and R⁴ are each, independently of one another, hydrogen,         methyl, ethyl or phenyl and R² and R³ and also R⁵ to R⁸ are         each, independently of one another, hydrogen or methyl.

Very particularly preferred ammonium ions (IVu) are those in which

-   -   R¹ to R³ are each, independently of one another, C₁-C₁₈-alkyl;         or     -   R¹ and R² are together 1,5-pentylene or 3-oxa-1,5-pentylene and         R³ is C₁-C₁₈-alkyl, 2-hydroxyethyl or 2-cyanoethyl.

Examples of tertiary amines from which the quaternary ammonium ions of the general formula (IVu) are derived from quaternation by the abovementioned radical R are diethyl-n-butylamine, diethyl-tert-butylamine, diethyl-n-pentylamine, diethylhexylamine, diethyloctylamine, diethyl(2-ethylhexyl)amine, di-n-propylbutylamine, di-n-propyl-n-pentylamine, di-n-propylhexylamine, di-n-propyloctylamine, di-n-propyl(2-ethyl-hexyl)amine, diisopropylethylamine, diisopropyl-n-propylamine, diisopropylbutylamine, diisopropylpentylamine, diisopropylhexylamine, diisopropyloctylamine, diisopropyl(2-ethylhexyl)amine, di-n-butylethylamine, di-n-butyl-n-propylamine, di-n-butyl-n-pentylamine, di-n-butylhexylamine, di-n-butyloctylamine, di-n-butyl(2-ethylhexyl)amine, N-n-butylpyrrolidine, N-sec-butylpyrrolidine, N-tert-butylpyrrolidine, N-n-pentylpyrrolidine, N,N-dimethylcyclohexylamine, N,N-diethylcyclohexylamine, N,N-di-n-butylcyclohexylamine, N-n-propylpiperidine, N-isopropylpiperidine, N-n-butylpiperidine, N-sec-butylpiperidine, N-tert-butylpiperidine, N-n-pentylpiperidine, N-n-butylmorpholine, N-sec-butylmorpholine, N-tert-butylmorpholine, N-n-pentylmorpholine, N-benzyl-N-ethylaniline, N-benzyl-N-n-propylaniline, N-benzyl-N-isopropylaniline, N-benzyl-N-n-butylaniline, N,N-dimethyl-p-toluidene, N,N-diethyl-p-toluidene, N,N-di-n-butyl-p-toluidene, diethylbenzylamine, di-n-propylbenzylamine, di-n-butylbenzylamine, diethylphenylamine, di-n-propylphenylamine and di-n-butylphenylamine.

Preferred tertiary amines (IVu) are diisopropylethylamine, diethyl-tert-butylamine, diisopropylbutylamine, di-n-butyl-n-pentylamine, N,N-di-n-butylcyclohexylamine and tertiary amines derived from pentyl isomers.

Particularly preferred tertiary amines are di-n-butyl-n-pentylamine and tertiary amines derived from pentyl isomers. A further preferred tertiary amine which has three identical radicals is triallylamine.

Very particularly preferred guanidinium ions (IVv) are those in which

-   -   R¹ to R⁵ are methyl.

Very particularly preferred cholinium ions (IVw) are those in which

-   -   R¹ and R² are each, independently of one another, methyl, ethyl,         1-butyl or 1-octyl and R³ is hydrogen, methyl, ethyl, acetyl,         —SO₂OH or —PO(OH)₂;     -   R¹ is methyl, ethyl, 1-butyl or 1-octyl, R² is a —CH₂—CH₂—OR⁴         group and R³ and R⁴ are each, independently of one another,         hydrogen, methyl, ethyl, acetyl, —SO₂OH or —PO(OH)₂; or     -   R¹ is a —CH₂—CH₂—OR⁴ group, R² is a —CH₂—CH₂—OR⁵ group and R³ to         R⁵ are each, independently of one another, hydrogen, methyl,         ethyl, acetyl, —SO₂OH or —PO(OH)₂.

Particularly preferred cholinium ions (IVw) are those in which R³ is selected from among hydrogen, methyl, ethyl, acetyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-meth-oxy-5,10-oxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

Very particularly preferred phosphonium ions (IVx) are those in which

-   -   R¹ to R³ are each, independently of one another, C₁-C₁₈-alkyl,         in particular butyl, isobutyl, 1-hexyl or 1-octyl.

Among the abovementioned heterocyclic cations, the pyridinium ions, pyrazolinium ions, pyrazolium ions and imidazolinium ions and also the imidazolium ions are preferred. Preference is likewise given to ammonium ions. The metal cations [M¹]⁺, [M²]+, [M³]⁺, [M⁴]²⁺ and [M⁵]³⁺ mentioned in the formulae (IIIa) to (IIIj) are generally metal cations of groups 1, 2, 6, 7, 8, 9, 10, 11, 12 and 13 of the Periodic Table. Suitable metal cations are, for example, Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Ba²⁺, Cr³⁺, Fe²⁺, Fe³⁺, Co²⁺, Ni²⁺, Cu²⁺, Ag⁺, Zn²⁺ and Al³⁺.

As anions, it is in principle possible to use all anions.

The anion [Y]^(n−) of the ionic liquid is, for example, selected from among

the group of halides and halogen compounds of the formulae:

F⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, PF₆ ⁻, AlCl ₄ ⁻, Al₂Cl₇ ⁻, Al₃Cl₁₀ ⁻, AlBr₄ ⁻, FeC₄ ⁻, BCl₄ ⁻, SbF₆ ⁻, AsF₆, ⁻ZnCl₃ ⁻, SnCl₃ ⁻, CUCl₂ ⁻, CF₃SO₃ ⁻, (CF₃SO₃)₂N⁻, CF₃CO₂ ⁻, CCl₃CO₂ ⁻, CN⁻, SCN⁻, OCN⁻

the group of sulfates, sulfites and sulfonates of the general formulae:

SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, HSO3⁻, R^(a)OSO₃ ⁻, R^(a)SO₃ ⁻

the group of phosphates of the general formulae

PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, R^(a)PO₄ ²⁻, HR^(a)PO₄ ⁻, R^(a)R^(b)PO₄ ⁻

the group of phosphonates and phosphinates of the general formulae:

R^(a)HPO₃ ⁻, R^(a)R^(b)PO₂ ⁻, R^(a)R^(b)PO₃ ⁻

the group of phosphites of the general formulae: PO₃ ³⁻, HPO₃ ²⁻, H₂PO₃ ⁻, R^(a)PO₃ ²⁻, R^(a)HPO3⁻, R^(a)R^(b)PO₃ ⁻

the group of phosphonites and phosphinites of the general formulae:

R^(a)R^(b)PO₂ ⁻, R^(a)HPO₂ ⁻, R^(a)R^(b)PO⁻, R^(a)HPO⁻

the group of carboxylic acids of the general formula:

R^(a)COO⁻

the group of borates of the general formulae:

BO₃ ³⁻, HBO₃ ²⁻, H₂BO₃ ⁻, R^(a)R^(b)BO₃ ⁻, R^(a)HBO₃ ⁻, R^(a)BO₃ ²⁻, B(OR^(a))(OR^(b))(OR^(c))(OR^(d))⁻, B(HSO₄)⁻, B(R^(a)SO4)⁻

the group of boronates of the general formulae:

R^(a)BO₂ ²⁻, R^(a)R^(b)BO⁻

the group of carbonates and carbonic esters of the general formulae:

HCO₃ ⁻, CO₃ ²⁻, R^(a)CO₃ ⁻

the group of silicates and silicic esters of the general formulae:

SiO₄ ⁻, HSiO₄ ³⁻, H₂SiO₄ ²⁻, H₃SiO₄ ⁻, R^(a)SiO₄ ³⁻, R^(a)R^(b)SiO₄ ²⁻, R^(a)R^(b)R^(c)SiO₄ ⁻, HR^(a)SiO₄ ²⁻, H₂R^(a)SiO₄ ⁻, HR^(a)R^(b)SiO₄ ⁻

the group of alkyl silane and aryl silane salts of the general formulae: R^(a)SiO₃ ³⁻, R^(a)R^(b)SiO₂ ²⁻, R^(a)R^(b)R^(c)SiO⁻, R^(a)R^(b)R^(c)SiO₃ ⁻, R^(a)R^(b)R^(c)SiO₂ ⁻, R^(a)R^(b)SiO₃ ²⁻

the group of carboximides, bis(sulfonyl)imides and sulfonylimides of the general formulae:

the group of methides of the general formula:

-   -   the group of alkoxides and aryloxides of the general formula         R^(a)O⁻;     -   the group of halometalates of the general formula         [M_(q)Hal_(r)]^(s−),         -   where M is a metal and Hal is fluorine, chlorine, bromine or             iodine, q and r are positive integers and indicate the             stoichiometry of the complex and s is a positive integer and             indicates the charge on the complex;

the group of sulfides, hydrogen sulfides, polysulfides, hydrogen polysulfides and thiolates of the general formulae:

-   -   S²⁻, HS⁻, [S_(v)]²⁻, [HS_(v)]⁻, [R^(a)S]⁻,     -   where v is a positive integer from 2 to 10;

the group of complex metal ions such as Fe(CN)₆ ³⁻, Fe(CN)₆ ⁴⁻, MnO₄ ⁻, Fe(CO)₄ ⁻.

Here, R^(a), R^(b), R^(c) and R^(d) are each, independently of one another, hydrogen, C₁-C₃₀-alkyl, C₂-C₁₈-alkyl which is optionally interrupted by one or more nonadjacent oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups, C₆-C₁₄-aryl, C₅-C₁₂-cycloalkyl or a five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle, where two of them may together form an unsaturated, saturated or aromatic ring which is optionally interrupted by one or more oxygen and/or sulfur atoms and/or one or more unsubstituted or substituted imino groups, where the radicals mentioned may each be additionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles.

Here, C₁-C₁₈-alkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example, methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, 2,4,4-trimethylpentyl, decyl, dodecyl, tetradecyl, headecyl, octadecyl, 1,1-dimethylpropyl, 1,1-dimethylbutyl, 1,1,3,3-tetramethylbutyl, benzyl, 1-phenylethyl, α,α-dimethylbenzyl, benzhydryl, p-tolylmethyl, 1-(p-butylphenyl)ethyl, p-chlorobenzyl, 2,4-dichlorobenzyl, p-methoxybenzyl, m-ethoxybenzyl, 2-cyanoethyl, 2-cyanopropyl, 2-methoxycarbonylthyl, 2-ethoxycarbonylethyl, 2-butoxycarbonylpropyl, 1,2-di-(methoxycarbonyl)ethyl, 2-methoxyethyl, 2-ethoxyethyl, 2-butoxyethyl, diethoxymethyl, diethoxyethyl, 1,3-dioxolan-2-yl, 1,3-dioxan-2-yl, 2-methyl-1,3-dioxolan-2-yl, 4-methyl-1,3-dioxolan-2-yl, 2-isopropoxyethyl, 2-butoxypropyl, 2-octyloxyethyl, chloromethyl, trichloromethyl, trifluoromethyl, 1,1-dimethyl-2-chloroethyl, 2-methoxyisopropyl, 2-eth-oxyethyl, butylthiomethyl, 2-dodecylthioethyl, 2-phenlythioethyl, 2,2,2-trifluoroethyl, 2-hydroxyethyl, 2-hydroxypropyl, 3-hydroxypropyl, 4-hydroxybutyl, 6-hydroxyhexyl, 2-aminoethyl, 2-aminopropyl, 4-aminobutyl, 6-aminohexyl, 2-methylaminoethyl, 2-methylaminopropyl, 3-methylaminopropyl, 4-methylaminobutyl, 6-methylaminohexyl, 2-dimethylaminoethyl, 2-dimethylaminopropyl, 3-dimethylaminopropyl, 4-dimethyl-aminobutyl, 6-dimethylaminohexyl, 2-hydroxy-2,2-dimethylethyl, 2-phenoxyethyl, 2-phenoxypropyl, 3-phenoxypropyl, 4-phenoxybutyl, 6-phenoxyhexyl, 2-methoxyethyl, 2-methoxypropyl, 3-methoxypropyl, 4-methoxybutyl, 6-methoxyhexyl, 2-ethoxyethyl, 2-ethoxypropyl, 3-ethoxypropyl, 4-ethoxybutyl or 6-ethoxyhexyl.

C₂-C₁₈-Alkyl which is optionally substituted by one or more nonadjacent oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups is, for example, 5-hydroxy-3-oxapentyl, 8-hydroxy-3,6-dioxaoctyl, 11-hydroxy-3,6,9-tri-oxaundecyl, 7-hydroxy-4-oxaheptyl, 11-hydroxy-4,8-dioxaundecyl, 15-hydroxy-4,8,12-trioxapentadecyl, 9-hydroxy-5-oxanonyl, 14-hydroxy-5,10-oxatetradecyl, 5-methoxy-3-oxapentyl, 8-methoxy-3,6-dioxaoctyl, 11-methoxy-3,6,9-trioxaundecyl, 7-methoxy-4-oxaheptyl, 11-methoxy-4,8-dioxaundecyl, 15-methoxy-4,8,12-trioxapentadecyl, 9-methoxy-5-oxanonyl, 14-methoxy-5,10-oxatetradecyl, 5-ethoxy-3-oxapentyl, 8-ethoxy-3,6-dioxaoctyl, 11-ethoxy-3,6,9-trioxaundecyl, 7-ethoxy-4-oxaheptyl, 11-ethoxy-4,8-dioxaundecyl, 15-ethoxy-4,8,12-trioxapentadecyl, 9-ethoxy-5-oxanonyl or 14-ethoxy-5,10-oxatetradecyl.

If two radicals form a ring, these radicals can together form, for example, 1,3-propylene, 1,4-butylene, 2-oxa-1,3-propylene, 1-oxa-1,3-propylene, 2-oxa-1,3-propenylene, 1-aza-1,3-propenylene, 1-C₁-C₄-alkyl-1-aza-1,3-propenylene, 1,4-buta-1,3-dienylene, 1-aza-1,4-buta-1,3-dienylene or 2-aza-1,4-buta-1,3-dienylene as fused-on building block.

The number of nonadjacent oxygen and/or sulfur atoms and/or imino groups is in principle not subject to any restrictions or is automatically restricted by the size of the radical or the cyclic building block. In general, it will be no more than 5 in the respective radical, preferably no more than 4 and very particularly preferably no more than 3. Furthermore, there is generally at least one carbon atom, preferably at least two carbon atoms, between any two heteroatoms.

Substituted and unsubstituted imino groups can be, for example, imino, methylimino, isopropylimino, n-butylimino or tert-butylimino.

For the purposes of the present invention, the term “functional groups” refers, for example, to the following: carboxy, carboxamide, hydroxy, di-(C₁-C₄-alkyl)amino, C₁-C₄-alkyloxycarbonyl, cyano or C₁-C₄-alkoxy. Here, C₁C₄-alkyl is methyl, ethyl, propyl, isopropyl, n-butyl, sec-butyl or tert-butyl.

C₆-C₁₄-Aryl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles is, for example, phenyl, tolyl, xylyl, α-naphthyl, β-naphthyl, 4-diphenylyl, chlorophenyl, dichlorophenyl, trichlorophenyl, difluorophenyl, methylphenyl, dimethylphenyl, trimethylphenyl, ethylphenyl, diethylphenyl, isopropylphenyl, tert-butylphenyl, dodecylphenyl, methoxyphenyl, dimethoxyphenyl, ethoxyphenyl, hexyloxyphenyl, methylnaphthyl, isopropyinaphthyl, chloronaphthyl, ethoxynaphthyl, 2,6-dimethylphenyl, 2,4,6-trimethylphenyl, 2,6-dimethoxyphenyl, 2,6-dichlorophenyl, 4-bromophenyl, 2- or 4-nitrophenyl, 2,4- or 2,6-dinitrophenyl, 4-dimethylaminophenyl, 4-acetylphenyl, methoxyethylphenyl or ethoxymethylphenyl.

C₅-C₁₂-Cycloalkyl which is optionally substituted by functional groups, aryl, alkyl, aryloxy, halogen, heteroatoms and/or heterocycles is, for example, cyclopentyl, cyclohexyl, cyclooctyl, cyclododecyl, methylcyclopentyl, dimethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl, diethylcyclohexyl, butylcyclohexyl, methoxycyclohexyl, dimethoxycyclohexyl, diethoxycyclohexyl, butylthiocyclohexyl, chlorocyclohexyl, dichlorocyclohexyl, dichlorocyclopentyl or a saturated or unsaturated bicyclic system such as norbornyl or norbornenyl.

A five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle is, for example, furyl, thiophenyl, pyryl, pyridyl, indolyl, benzoxazolyl, dioxolyl, dioxyl, benzimidazolyl, benzthiazolyl, dimethylpyridyl, methylquinolyl, dimethylpyryl, methoxyfuryl, dimethoxypyridyl, difluoropyridyl, methylthiophenyl, isopropylthiophenyl or tert-butylthiophenyl.

Preferred anions are selected from the group of halides and halogen-comprising compounds, the group of carboxylic acids, the group of sulfates, sulfites and sulfonates and the group of phosphates.

Preferred anions are chloride, bromide, iodide, SCN⁻, OCN⁻, CN⁻, acetate, C₁-C₄-alkylsulfates, R^(a)—COO⁻, R^(a)SO₃ ⁻, R^(a)R^(b)PO₄ ⁻, methanesulfonates, tosylate, C₁-C₄ dialkylphosphates, hydrogen sulfate or tetrachloroaluminate.

Particularly preferred anions are Cl⁻, CH₃COO⁻ or CH₃SO₃ ⁻.

Both cations and anions are present in the ionic liquid. Within the ionic liquid, a proton or an alkyl radical is transferred from the cation to the anion. This forms two uncharged molecules. There is thus an equilibrium in which anions, cations and the two uncharged molecules formed therefrom are present.

The solution preferably has a temperature of not more than 180° C. The solution of the present invention more preferably has a temperature of not more than 160° C., even more preferably not more than 120° C. and particularly preferably not more than 100° C.

The present invention further provides a process for preparing a solution according to the invention, which comprises the steps

-   -   a) addition of cellulose to a solution comprising an ionic         liquid comprising anions and cations as solvent, wherein the         cations comprise at least one nitrogen atom which is present in         protonated form as ammonium cation     -   b) mixing of the solution until the cellulose is completely         dissolved.

Mixing is preferably carried out by means of stirring, shaking and/or with the aid of microwaves.

The dissolution preferably occurs within 3 days, more preferably within one day and particularly preferably within 12 hours.

The present invention further provides for the use of a solution according to the present invention for the physical or chemical treatment of cellulose.

The chemical treatment can comprise oxidation, reduction, pyrolysis, hydrolysis, isomeration, sterification, alkoxylation or copolymerization.

The present invention is illustrated by means of the following examples.

EXAMPLES Example 1

0.78 g of newsprint are cut into pieces having a size of about 1 cm², admixed with 10.0 g of 1-methylimidazole hydrochloride (1-methylimidazolium chloride) and stirred at 120° C. After 23 hours, the paper has dissolved completely.

Example 2

7.8 g of filter paper (blue band filter) are cut into pieces having a size of about 1 cm², admixed with 100 g of 1-methylimidazol hydrochloride and stirred at 95° C. After 72 hours, the paper has dissolved completely. 

1. A solution comprising cellulose and an ionic liquid comprising anions and cations as solvent, wherein the cations comprise at least one atom selected from the group consisting of nitrogen, oxygen, sulfur and phosphorus which is present in protonated form.
 2. The solution according to claim 1, wherein the cations comprise at least one nitrogen atom which is present in protonated form as an ammonium cation.
 3. The solution according to claim 1, wherein said solution comprises more than 1% by weight of cellulose, based on the total weight of the solution.
 4. The solution according to claim 1, wherein said anions and cations form a salt of general formula (I) [A]_(n) ⁺ [Y]^(n−)  (I), where n is 1, 2, 3 or 4, [A]⁺ is a quaternary ammonium cation, an oxonium cation, a sulfonium cation or a phosphonium cation and [Y]^(n−) is a monovalent, divalent, trivalent or tetravalent anion; or mixed salts of general formulae (II) [A ¹]⁺ [A ²]⁺ [Y] ^(n−)  (IIa), where n=2; [A ¹]⁺ [A ²]⁺ [A ³]⁺ [Y] ^(n−)  (IIb), where n=3; [A ¹]⁺ [A ²]⁺ [A ³]⁺ [A ⁴]⁺ [Y] ^(n−)  (IIc), where n=4, and where [A¹]⁺, [A²]⁺, [A³]⁺ and [A⁴]⁺ are selected independently from among the groups mentioned for [A]⁺, and [Y]^(n−) is as defined under (A); or mixed salts of general formulae (III) [A ¹]⁺ [A ²]⁺ [A ³]⁺ [M ¹]⁺ [Y] ^(n−)  (IIIa), where n=4; [A ¹]⁺ [A ²]⁺ [M ¹]⁺ [M ²]⁺ [Y] ^(n−)  (IIIb), where n=4; [A ¹]⁺ [M ¹]⁺ [M ²]⁺ [M ³]⁺ [Y] ^(n−)  (IIIc), where n=4; [A ¹]⁺ [A ²]⁺ [M ¹]⁺ [Y] ^(n−)  (IIId), where n=3; [A ¹]⁺ [M ¹]⁺ [M ²]⁺ [Y] ^(n−)  (IIIe), where n=3; [A ¹]⁺ [M ¹]⁺ [Y] ^(n−)  (IIIf), where n=2; [A ¹]⁺ [A ²]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIg), where n=4; [A ¹]⁺ [M ¹]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIh), where n=4; [A ¹]⁺ [M ⁵]³⁺ [Y] ^(n−)  (IIIi), where n=4; or [A ¹]⁺ [M ⁴]²⁺ [Y] ^(n−)  (IIIj), where n=3, and where [A¹]⁺, [A²]⁺ and [A³]⁺ are selected independently from among the groups mentioned for [A]⁺, [Y]^(n−) is as defined under (A) and [M¹]⁺, [M²]⁺, [M³]⁺ are monovalent metal cations, [M⁴]²⁺ is a divalent metal cation and [M⁵]³⁺ is a trivalent metal cation.
 5. The solution according to claim 1, wherein the ionic liquid comprises at least one cation selected from the group consisting of cations of formulae (IVa) to (IVy):

and oligomers comprising these structures, where the radical R is hydrogen; and the radicals R¹ to R⁹ are each, independently of one another, hydrogen, a sulfo group or a carbon-comprising organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical which has from 1 to 20 carbon atoms and is unsubstituted or interrupted by from 1 to 5 heteroatoms or functional groups or substituted, with the radicals R¹ to R⁹ which are bound to a carbon atom (and not to a heteroatom) in the abovementioned formulae (IV) also being able to be halogen or a functional group; or two adjacent radicals from the group consisting of R¹ to R⁹ can together also be a divalent, carbon-comprising organic, saturated or unsaturated, acyclic or cyclic, aliphatic, aromatic or araliphatic radical which has from 1 to 30 carbon atoms and is unsubstituted or interrupted by from 1 to 5 heteroatoms or functional groups or substituted.
 6. The solution according to claim 1, wherein the ionic liquid comprises at least one anion selected from the group consisting of the group of halides and halogen compounds of the formulae: F⁻, Cl⁻, Br⁻, I⁻, BF₄ ⁻, PF₆ ⁻, AlCl₄ ⁻, Al₂Cl₇ ⁻, Al₃Cl₁₀ ⁻, AlBr₄ ⁻, FeCl₄ ⁻, BCl₄ ⁻, SbF₆ ⁻, AsF₆, ZnCl₃ ⁻, SnCl₃ ⁻, CuCl₂ ⁻, CF₃SO₃ ⁻, (CF₃SO₃)₂N⁻, CF₃CO₂ ⁻, CCl₃CO₂ ⁻, CN⁻, SCN⁻, OCN⁻ the group of sulfates, sulfites and sulfonates of the general formulae: SO₄ ²⁻, HSO₄ ⁻, SO₃ ²⁻, HSO₃ ⁻, R^(a)OSO₃ ⁻, R^(a)SO₃ ⁻ the group of phosphates of the general formulae PO₄ ³⁻, HPO₄ ²⁻, H₂PO₄ ⁻, R^(a)PO₄ ²⁻, HR^(a)PO₄ ⁻, R^(a)R^(b)PO₄ ⁻ the group of phosphonates and phosphinates of the general formulae: R^(a)HPO₃ ⁻, R^(a)R^(b)PO₂ ⁻, R^(a)R^(b)PO₃ ⁻ the group of phosphites of the general formulae: PO₃ ³⁻, HPO₃ ²⁻, H₂PO₃ ⁻, R^(a)PO₃ ²⁻, R^(a)HPO₃ ⁻, R^(a)R^(b)PO₃ ⁻ the group of phosphonites and phosphinites of the general formulae: R^(a)R^(b)PO₂ ⁻, R^(a)HPO₂ ⁻, R^(a)R^(b)PO⁻, R^(a)HPO⁻ the group of carboxylic acids of the general formula: R^(a)COO⁻ the group of borates of the general formulae: BO₃ ³⁻, HBO₃ ²⁻, H₂BO₃ ⁻, R^(a)R^(b)BO₃ ⁻, R^(a)HBO₃ ⁻, R^(a)BO₃ ²⁻, B(OR^(a))(OR^(b))(OR^(c))(OR^(d))⁻, B(HSO₄)⁻, B(R^(a)SO4)⁻ the group of boronates of the general formulae: R^(a)BO₂ ²⁻, R^(a)R^(b)BO⁻ the group of carbonates and carbonic esters of the general formulae: HCO₃ ⁻, CO₃ ²⁻, R^(a)CO₃ ⁻ the group of silicates and silicic esters of the general formulae: SiO₄ ⁴⁻, HSiO₄ ³⁻, H₂SiO₄ ²⁻, H₃SiO₄ ⁻, R^(a)SiO₄ ³⁻, R^(a)R^(b)SiO₄ ²⁻, R^(a)R^(b)R^(c)SiO₄ ⁻, HR^(a)SiO₄ ², H₂R^(a)SiO₄ ⁻, HR^(a)R^(b)SiO₄ ⁻ the group of alkyl silane and aryl silane salts of the general formulae: R^(a)SiO₃ ³⁻, R^(a)R^(b)SiO₂ ²⁻, R^(a)R^(b)R^(c)SiO⁻, R^(a)R^(b)R^(c)SiO₃ ⁻, R^(a)R^(b)R^(c)SiO₂ ⁻, R^(a)R^(b)SiO₃ ²⁻ the group of carboximides, bis(sulfonyl)imides and sulfonylimides of the general formulae:

the group of methides of the general formula:

the group of alkoxides and aryloxides of the general formula R^(a)O⁻; the group of halometalates of the general formula [M_(q)Hal_(r)]^(s−), where M is a metal and Hal is fluorine, chlorine, bromine or iodine, q and r are positive integers and indicate the stoichiometry of the complex and s is a positive integer and indicates the charge on the complex, the group of sulfides, hydrogen sulfides, polysulfides, hydrogen polysulfides and thiolates of the general formulae: S²⁻, HS⁻, [S_(v)]²⁻, [HS_(v)]⁻, [R^(a)S]⁻, where v is a positive integer from 2 to 10, and the group of complex metal ions such as Fe(CN)₆ ³⁻, Fe(CN)₆ ⁴⁻, MnO₄ ⁻, Fe(CO)₄ ⁻, where R^(a), R^(b), R^(c) and R^(d) are each, independently of one another, hydrogen, C₁-C₁₈-alkyl, C₂-C₁₈-alkyl which is optionally interrupted by one or more nonadjacent oxygen and/or sulfur atoms and/or one or more substituted or unsubstituted imino groups, C₆-C₁₄-aryl, C₅-C₁₂-cycloalkyl or a five- or six-membered, oxygen-, nitrogen- and/or sulfur-comprising heterocycle, where two of them may together form an unsaturated, saturated or aromatic ring which is optionally interrupted by one or more oxygen and/or sulfur atoms and/or one or more unsubstituted or substituted imino groups, where the radicals mentioned may each be additionally substituted by functional groups, aryl, alkyl, aryloxy, alkyloxy, halogen, heteroatoms and/or heterocycles.
 7. The solution according to claim 1 which has a temperature of not more than 180° C.
 8. A process for preparing a solution according to claim 1, which comprises the steps of a) addition of adding cellulose to a solution comprising an ionic liquid comprising anions and cations as solvent, wherein the cations comprise at least one nitrogen atom which is present in protonated form as an ammonium cation, and b) mixing of the solution until the cellulose is completely dissolved.
 9. A method for the physical or chemical treatment of cellulose comprising the use of an ionic liquid comprising anions and cations as solvent, wherein the cations comprise at least one atom selected from the group consisting of nitrogen, oxygen, sulfur, and phosphorus which is present in protonated form. 